Process and composition for treatment of magnesium prior to spot welding



Patented Apr. 6, 1954 r 2,674,523 PROCESS AND COMPOSITION FOR TREAT- MENT OF MAGNESI WELDING UM PRIOR TO SPOT Louis McDonald, Altadena, and Alfred E. Hawley, Long Beach, Calif., asslgnors to Kelite Products, Inc., Los Angeles, Calif fornia a corporation of Cali- No Drawing. Application April 24, 1953,

Serial No. 351,054

7 Claims.

nesium is much too reactive a metal to be etched by the aqueous baths now employed for etching aluminum and aluminum alloys. Accordingly the cleaning of magnesium surfaces prior to spot welding has heretofore been carried out by the use of steel wool.

It is a general object of the present invention to provide a composition and process for cleaning magnesium prior to spot welding through the use of an aqueous etching material.

The composition and process of the present inpresent invention is an aqueous material including certain acidic etching ingredients and certain sequestering agents or organic reducing agents. The acidic etching agents, or some thereof, are materials of viscous nature and having the property of confining its action in the etching composition to the surface of the magnesium are ticle to be etched. Such viscous acid etching agents are provided by the use of polystyrene sulfonic acids. These polystyrene sulfonic acids in the composition have a property of etching the coating on the magnesium article without allowing, however, a deep penetration of the etching composition into the surface so that the activity of the acidic composition is confined only to the coating which is desired to be etched and removed. The polystyrene sulfonic acids employed are producable in either of two ways, i. e., through either first polymerizing styrene and then sulfonating the same, or by first sulfonatingstyrene and then polymerizing it, the latter being the preferred method. It is principally the molecular weight of the polystyrene molecule which deterpolymerized it is easier to produce a polystyrene viscosity than is the case where the styrene is first polymerized and then sulfonated. The process of sulfonating polystyrene alters the molecular weight.

The acidic etching composition also includes an aryl sulionic acid, those having less than four alkyl carbon atoms being found usable, such as benzene, toluene or xylene sulfonic acids. The sulfonic acids employed, both the polystyrene acid and aryl sulfonic acid, are thought to etch the surface coating from magnesium articles by hydrolizing to some extent to release sulfuric acid in active form, the activity of which is confined to the surface coating because of the viscosity and low penetrating properties of the composition.

droxy carboxylic acids are citric acid, tartaric acid, gluconic acid, glucona deltalactone, as well as the sodium or ammonia compounds thereof.

In the art the effectiveness of a process of the surface resistance of the coating to about 20 to 40 micro-ohms in about five or ten minutes of treatment.

tory for spot welding and therefore the process and composition of the present invention are enabled to satisfactorily clean magnesium surfaces for spot welding without the necessity of the use of steel wool, which is the present practice.

The composition and process of the present invention, together with further advantages of the invention, will be understood from the following description of a preferred composition and process. A preferred composition comprises:

Per cent Xylene sulfonic acid 28 Baum ammonia 0.5

Glucona delta lactone 6.75

Polystyrene sulfonic acid '6 Water 81.75

In the foregoing preferred composition any aryl sulfonic acid with less than four alkyl carbon atoms may be substituted for the xylene sulfonic acid, such as benzene sulfonic acid, toluene sulfonic acid and the aryl sulfonic acid content may vary within the range of from 2% to 10%. In the composition any water soluble aliphatic hydroxy carboxylic acid, such as citricacid, tartaric acid, or gluconic acid, may be substituted for the glucona delta lactone and the quantity of such sequestering agent may vary in the composition from 5% to 25%.

The 28 Baum ammonia is employed in the composition since it has some beneficial effect in the desired sequestering action but may be omitted when desired. In the preferred composition the ammonia content is about 0.2% but it may vary when employed within the limits of about 0.1% to 1.7%, and in addition thereto or alternately the composition may include equivalent amounts of the sodium ion, either introduced into the composition by employing the sodium salts of the water soluble aliphatic hydroxy carboxylic acid in place of the acid itself, or in any other manner. The polystyrene sulfonic acid in the composition may vary in the range of 2% to and the most desirable viscous properties of the solution, as well as the etching properties, are obtained when using polystyrene sulionic acids having molecular weights in the order of 20,000 to 250,000.

While the particular composition and process herein described for etching and cleaning magnesium preparatory to spot welding are well adapted to carry out the objects of the present invention, this invention is of the scope set forth in the appended claims.

We claim:

1. A composition for cleaning magnesium which comprises, a viscous aqueous solution including essentially polystyrene sulfonic acid and aryl sulfonic acid having less than 4 alkyl carbon atoms and a water soluble aliphatic hydroxy carboxylic acid sequestering agent.

2. A composition for cleaning magnesium 6 which comprises, a viscous aqueous solution including essentially polystyrene sulfonic acid and aryl sulfonic acid having less than 4 alkyl carbon atoms and a water soluble aliphatic hydroxy carboxylic acid sequestering agent, the proportions of polystyrene sulfonic acid being between 2% and 10 the sequestering agent employed being between 5% and 25%, the aryl sulfonic acid being between 2% and 10%.

3. A composition for cleaning magnesium which comprises, a viscous aqueous solution including essentially polystyrene sulfonic acid and aryl sulfonic acid having less than 4 alkyl carbon atoms and a water soluble aliphatic hydroxy carboxylic acid sequestering agent, the composition also including ammonia.

4. A composition for cleaning magnesium which comprises, a viscous aqueous solution including essentially polystyrene sulfonic acid and aryl sulfonic acid having less than 4 alkyl carbon atoms and a water soluble aliphatic hydroxy carboxylic acid sequestering agent, the proportions of polystyrene sulfonic acid being between 2% and 10%, the sequestering agent employed being between 5% and 25%, the aryl sulfonic acid being between 2% and 10%, the composition also including ammonia from 0.1% to 1.7%.

5. A process of cleaning magnesium prior to spot welding which process comprises, applying to the surface to be spot welded a viscous etching composition, which viscous etching composition is an aqueous composition including essentially polystyrene sulfonic acid and aryl sulfonic acid of less than 4 alkyl carbon atoms, and a water soluble aliphatic hydroxy carboxylic acid sequestering agent.

6. A process of cleaning magnesium prior to spot welding which process comprises, applying to the surface to be spot welded a viscous etching composition, which viscous etching composition is an aqueous composition including essentially polystyrene sulfonic acid and aryl sulfonic acid of less than 4 alkyl carbon atoms, and a water soluble aliphatic hydroxy carboxylic acid sequestering agent, the proportions of polystyrene sulfonic acid being between 2% and 10%, the sequestering agent being between 5% and 25%, the aryl sulfonic acid being between 2% and 10%.

1. A process of cleaning magnesium prior to spot welding which process comprises, applying to the surface to be spot welded a viscous etching composition, which viscous etching composition is an aqueous composition including essentially polystyrene sulfonic acid and aryl sulfonic acid of less than 4 alkyl carbon atoms, and a water soluble aliphatic hydroxy carboxylic acid sequestering agent, the .composition also including ammonia.

References Cited in the file of this patent UNITED STATES PATENTS 

5. A PROCESS OF CLEANING MAGNESIUM PRIOR TO SPOT WELDING WHICH PROCESS COMPRISES, APPLYING TO THE SURFACE TO BE SPOT WELDED A VISCOUS ETCHING COMPOSITION, WHICH VISCOUS ETCHING COMPOSITION IS AN AQUEOUS COMPOSITION INCLUDING ESSENTIALLY POLYSTYRENE SULFONIC ACID AND ARYL SULFONIC ACID OF LESS THAN 4 ALKYL CARBON ATOMS, AND A WATER SOLUBLE ALIPHATIC HYDROXY CARBOXYLIC ACID SEQUESTERING AGENT. 